TodoMVC: Escape key with Firefox

[slegrand45]

When a todo entry is edited, the user must be able to press the escape key in order to cancel the modifications.

With Firefox 50 on FreeBSD, the escape key is correctly detected (the which field is equal to 27) but the input is never reset to the backup value. If the escape key is replaced by the "a" key for instance, it works ok.

With Chromium 54 on FreeBSD, the escape key works correctly. Nonetheless, it seems that Chromium fires two events: a keypress followed by a blur. While Firefox fires only the keypress event.